The present invention relates to methods and systems for transferring data between a plurality of storage devices, and more particularly to methods and systems for transferring data between the plurality storage devices without a host computer issuing an access request to a storage device being aware of the data transfer process.
There has been a data transfer control technique as used in a storage device subsystem such as a disk array subsystem in which a plurality of volumes are controlled by a controller, that frequently accessed data is transferred to a quickly accessible volume and infrequently accessed data is transferred to a slowly accessible volume. U.S. Patent Application Publication No. 2001/0054133 also discloses a technique for efficient data transfer concerning a system in which a volume used by an application is provided over a plurality of storage areas which are controlled by different controllers. According to this technique, data in a volume which is used by a specific application is transferred preferentially.
Data transfer in a storage device subsystem is executed by a controller which controls the storage device subsystem, and the controller can hide the data transfer process from a host computer connected with it. However, this method does not take into consideration data transfer which takes place over more than one storage device subsystem. Therefore, if data stored in a certain storage device subsystem is to be transferred to another storage device subsystem, the controller must inform the host computer that, in data transfer, the storage device subsystem to be accessed will change, which means that it is impossible to hide the data transfer process from the host computer. Also, U.S. Patent Application Publication No. 2001/0054133 does not disclose any technique of hiding such data transfer process from the host computer. Consequently, for data transfer, the host computer must stop its operation once and specify the storage device or volume to be accessed again.
Recently as data communications in companies have been explosively increasing, demand for continuous, around-the-clock access to storage devices has been growing. Taking this situation into account, it is expected that data transfer between a plurality of storage devices will have to be handled more and more frequently in the future. Thus, there is a growing need for a technique that enables data transfer between storage devices without interrupting operation of the host computer.
When a controller which manages the storage area of a storage device and forwards an access request from the host computer to the storage area is replaced or newly installed, the host computer deems that the storage area to, be accessed has been changed, and has to once stop its operation and specify the storage area to be accessed again as when data transfer between a plurality of storage devices takes place.